This adds a port to Linux on the IBM Z platform (a.k.a s390x). It only
supports the 64-bit ABI. Most functionality is working and all the tests
pass with the exception of the coredump tests*.
Unwinding is only supported if DWARF unwind information is present.
libunwind can't currently make use of the backchain (if present).
The getcontext/setcontext functions only preserve/restore a subset of
registers. Currently this only consists of callee-saved registers and
some parameter registers.
Vector registers and access registers are not saved (and aren't callee-
saved) by getcontext and cannot currently be modified. They will however
be restored unmodified after resuming a context from a signal handler.
There is no special libunwind support for setjmp, the functionality is
emulated using glibc (I think all the ports do this for modern Linux
kernels).
* Unwinding on s390x requires floating point register access which the
coredump library doesn't currently support.
Add support for the 32bit SuperH architecture running Linux.
Specifically, support is added for SH4, and support for earlier SH
versions and to the 64bit SH5 are left out. This was tested in qemu with
a little-endian SH4 debian image & GCC 4.7 cross compiler.
